1. Field of the Invention
The present invention relates to a thermal transfer sheet and an ink ribbon, in particular, to a thermal transfer sheet that has excellent capability of peeling at the interface between a non-transferable peeling layer and a protective layer and can impart high glossiness to printed matter.
2. Description of the Related Art
A protective layer composed of a thermoplastic resin is laminated on an image formed on a printing paper sheet, for example, an ink image formed by a sublimation thermal-transfer method using a sublimation or thermal diffusion dye. When such a protective layer is made to have a gas barrier property or an ultraviolet absorbing property, discoloration of an image covered with the protective layer can be suppressed and migration of ink forming the image to other articles containing plasticizers such as erasers can be suppressed.
A protective layer can be laminated on an ink image, for example, with a thermal transfer sheet. Such a thermal transfer sheet has a configuration in which a non-transferable peeling layer, a protective layer, and an adhesive layer are stacked on a sheet substrate in this order from the sheet substrate side of the thermal transfer sheet. By partially heating and pressing the sheet substrate side of the thermal transfer sheet, the protective layer corresponding to the heated part is transferred together with the adhesive layer as a protective laminate onto a printing paper sheet.
A thermal transfer sheet having a configuration in which a protective layer composed of a first resin and an adhesive layer composed of a second resin are stacked and 1.5 is the boundary value between the refractive index of the first resin and the refractive index of the second resin has been proposed (Japanese Unexamined Patent Application Publication No. 2006-12486). This is intended to suppress generation of rainbow unevenness (interference pattern) caused by the small thickness of a protective laminate that is to be transferred onto a printing paper sheet and is constituted by the protective layer and the adhesive layer.